Applicant?s Description: Hormone replacement therapy (HRT) in women is commonly used to diminish the physical symptoms of menopause and to reduce the risk of disorders such as osteoporosis, heart disease, and atherosclerosis. HRT may have by its own risks, in particular, an increased chance of developing endometrial or breast cancer. In an effort to reduce these risks, some physicians are prescribing the selective estrogen receptor modulator (SERM) raloxifene (trade name Evista) for the prevention of osteoporosis. Estrogen also has cognition-enhancing capabilities in postmenopausal women and may serve to prevent or delay the onset of Alzheimer?s disease. Because raloxifene can function as either an agonist or antagonist at estrogen receptors, it is not known whether it too may affect cognitive function. The goals of this study are to examine the cognitive function of women in the perimenopausal period and to compare the effects of estrogen replacement and raloxifene treatment on cognitive function. The women in the two replacement groups will be compared with same-aged women who are still menstruating and to same-aged postmenopausal women who are not on HRT. The research will therefore compare the function of age-matched women with cyclic variation in estrogen levels (premenopausal), consistently high estrogen levels (postmenopausal, HRT-estrogen), consistently high SERM levels (postmenopausal, HRT-raloxifene), and consistently low estrogen levels (postmenopausal, no HRT). The tests will assess verbal recall and mental rotation skills, cognitive abilities that are influenced by estrogen levels. Digit span and Trail-Making Test performance, skills for which there is little evidence of an estrogen effect, will also be measured.